Surface treatment of silica-coated phosphor particles and method for a CRT screen

ABSTRACT

A method of surface-treating dry-powdered phosphor particles to control the triboelectric charge characteristics thereof includes the steps of providing the phosphor particles with a first coating of silica, dissolving a coupling agent selected from the group consisting of silanes and titanates in a suitable solvent to form a mixture, surface-coating the silica-coated phosphor particles with the mixture to provide a second coating of the coupling agent on the phosphor particles, filtering the surface-treated particles, rinsing the surface-treated particles with the solvent, and drying the surface-treated particles. The resultant dry-powdered surface-treated phosphor particles are used to make a luminescent viewing screen for a CRT. The coupling agent overlying the silica coating controls the triboelectric charging characteristics of the phosphor particles during the electrophotographic manufacturing of the screen.

The present invention relates to electrophotographically manufacturing aviewing screen for a cathode-ray tube (CRT), and more particularly to amethod of surface-treating dry-powdered phosphor particles with acoupling agent to control the triboelectric charging characteristicsthereof.

BACKGROUND OF THE INVENTION

A conventional shadow-mask-type CRT comprises an evacuated envelopehaving therein a viewing screen comprising an array of phosphor elementsof three different emission colors arranged in a cyclic order, means forproducing three convergent electron beams directed towards the screen,and a color selection structure or shadow mask comprising a thinmultiapertured sheet of metal precisely disposed between the screen andthe beam-producing means. The apertured metal sheet shadows the screen,and the differences in convergence angles permit the transmittedportions of each beam to selectively excite phosphor elements of thedesired emission color. A matrix of light-absorptive material surroundsthe phosphor elements.

In one prior process for forming each array of phosphor elements on aviewing faceplate of the CRT, the inner surface of the faceplate iscoated with a slurry of a photosensitive binder and phosphor particlesadapted to emit light of one of the three emission colors. The slurry isdried to form a coating, and a light field is projected from a sourcethrough the apertures in the shadow mask and onto the dried coating, sothat the shadow mask functions as a photographic master. The exposedcoating is subsequently developed to produce the first color-emittingphosphor elements. The process is repeated for the second and thirdcolor-emitting phosphor elements, utilizing the same shadow mask, butrepositioning the light source for each exposure. Each position of thelight source approximates the convergence angle of one of the electronbeams which excites the respective color-emitting phosphor elements. Amore complete description of this process, known as thephotolithographic wet process, can be found in U.S. Pat. No. 2,625,734,issued to H. B. Law on Jan. 20, 1953.

A drawback of the above-described wet process is that it may not becapable of meeting the higher resolution demands of the next generationof entertainment devices and the even higher resolution requirements formonitors, work stations and applications requiring color alpha-numerictext. Additionally, the wet photolithographic process (including matrixprocessing) requires 182 major processing steps, necessitates extensiveplumbing and the use of clean water, requires phosphor salvage andreclamation, and utilizes large quantities of electrical energy forexposing and drying the phosphor materials.

U.S. Pat. No. 3,475,169, issued to H. G. Lange on Oct. 28, 1969,discloses a process for electrophotographically screening colorcathode-ray tubes. The inner surface of the faceplate of the CRT iscoated with a volatilizable conductive material and then overcoated witha layer of volatilizable photoconductive material. The photoconductivelayer is then uniformly charged, selectively exposed with light throughthe shadow mask to establish a latent charge image, and developed usinga high molecular weight carrier liquid. The carrier liquid bears, insuspension, a quantity of phosphor particles of a given emissive colorthat are selectively deposited onto suitably charged areas of thephotoconductive layer, to develop the latent image. The charging,exposing and deposition process is repeated for each of the threecolor-emissive phosphors, i.e., green, blue, and red, of the screen. Animprovement in electrophotographic screening is described in U.S. Pat.No. 4,448,866, issued to H. G. Olieslagers et al. on May 15, 1984. Inthat patent, phosphor particle adhesion is said to be increased byuniformly exposing, with light, the portions of the photoconductivelayer lying between adjacent portions of the deposited pattern ofphosphor particles after each deposition step, so as to reduce ordischarge any residual charge and to permit a more uniform recharging ofthe photoconductor for subsequent depositions. Because the latter twopatents disclose an electrophotographic process that is, in essence, awet process, many of the drawbacks described above, with respect to thewet photolithographic process of U.S. Pat. No. 2,625,734, also areapplicable to the wet electrophotographic process.

Copending patent applications filed concurrently herewith, entitledMETHOD OF ELECTROPHOTOGRAPHICALLY MANUFACTURING A LUMINESCENT SCREENASSEMBLY FOR A CATHODE-RAY TUBE, and METHOD OF SURFACE TREATMENT OFCARRIER BEADS FOR USE IN ELECTROPHOTOGRAPHIC SCREEN PROCESSING,respectively describe an improved process for manufacturing CRT screenassemblies using triboelectrically charged, dry-powdered screenstructure materials, and surface-treated carrier beads having a couplingagent thereon to control the polarity and magnitude of the impartedcharge. The above-identified copending patent applications are assignedto the assignee of the present invention and incorporated by referenceherein for the purpose of disclosure. Applicants have determined thatwhile CRT viewing screens can be electrophotographically manufacturedusing untreated phosphor particles, surface treatment of the phosphorparticles increase the triboelectric charge on the phosphor particles,thereby causing a greater quantity of phosphor particles to be attachedto each carrier bead. This improves the efficiency of the dryelectrophotographic process and increases, by a factor of about 2 to 9times, the screen weight for screens manufactured using surface-treatedphosphors.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method of surface-treatingdry-powdered phosphor particles for use in manufacturing a viewingscreen for a CRT, to control the triboelectric charge characteristicsthereof, includes the steps of providing the phosphor particles with afirst coating of silica; dissolving a coupling agent selected from thegroup consisting of silanes and titanates in a suitable solvent to forma mixture; surface-coating the silica-coated phosphor particles with themixture to provide a second coating of the coupling agent on thephosphor particles; filtering the surface-treated particles; rinsing thesurface-treated particles with the solvent and drying thesurface-treated particles. The resultant dry-powdered surface-treatedphosphor particles are used to make a luminescent viewing screen for aCRT. The coupling agent overlying the silica coating controls thetriboelectric charging characteristics of the phosphor particles duringthe electrophotographic manufacturing of the screen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view, partially in axial section of a color cathode-raytube made according to the present invention.

FIG. 2 is a section of a screen assembly of the tube shown in FIG. 1.

FIGS. 3a through 3e show various steps in the manufacturing of the tubeshown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a color CRT having a glass envelope 11 comprising arectangular faceplate panel 12 and a tubular neck 14 connected by arectangular funnel 15. The funnel 15 has an internal conductive coating(not shown) that contacts an anode button 16 and extends into the neck14. The panel 12 comprises a viewing faceplate or substrate 18 and aperipheral flange or sidewall 20, which is sealed to the funnel 15 by aglass frit 21. A three color phosphor screen 22 is carried on the innersurface of the faceplate 18. The screen 22, shown in FIG. 2, preferablyis a line screen which includes a multiplicity of screen elementscomprised of red-emitting, green-emitting and blue-emitting phosphorstrips R, G and B, respectively, arranged in color groups of threestripes or triads in a cyclic order and extending in a direction whichis generally normal to the plane in which the electron beams aregenerated. In the normal viewing position for this embodiment, thephosphor stripes extend in the vertical direction. Preferably, thephosphor stripes are separated from each other by a light-absorptivematrix material 23, as is known in the art. Alternatively, the screencan be a dot screen. A thin conductive layer 24, preferably of aluminum,overlies the screen 22 and provides a means for applying a uniformpotential to the screen as well as reflecting light, emitted from thephosphor elements, through the faceplate 18. The screen 22 and theoverlying aluminum layer 24 comprise a screen assembly.

Again with respect to FIG. 1, a multi-apertured color selectionelectrode or shadow mask 25 is removably mounted, by conventional means,in predetermined spaced relation to the screen assembly. An electron gun26, shown schematically by the dashed lines in FIG. 1, is centrallymounted within the neck 14, to generate and direct these electron beams28 along convergent paths, through the apertures in the mask 25, to thescreen 22. The gun 26 may be, for example, a bi-potential electron gunof the type described in U.S. Pat. No. 4,620,133, issued to Morrell etal. on Oct. 28, 1986, or any other suitable gun.

The tube 10 is designed to be used with an external magnetic deflectionyoke, such as yoke 30 located in the region of the funnel-to-neckjunction. When activated, the yoke 30 subjects the three beams 28 tomagnetic fields which cause the beams to scan horizontally andvertically in a rectangular raster over the screen 22. The initial planeof deflection (at zero deflection) is shown by the line P--P in FIG. 1,at about the middle of the yoke 30. For simplicity, the actualcurvatures of the deflection beam paths in the deflection zone are notshown.

The screen 22 is manufactured by a novel electrophotographic processthat is schematically represented in FIGS. 3a through 3e and describedin the former above-identified copending patent application. Initially,the panel is washed with a caustic solution, rinsed with water, etchedwith buffered hydrofluoric acid and rinsed once again with water, as isknown in the art. The inner surface of the viewing faceplate 18 is thencoated with a layer 32 of an electrically conductive material whichprovides an electrode for an overlying photoconductive layer 34. Theconductive layer 32 is coated with the photoconductive layer 34,comprising a volatilizable organic polymeric material, a suitablephotoconductive dye and a solvent. The composition and method of formingthe conductive layer 32 and the photoconductive layer 34 are describedin the former above-identified copending patent application.

The photoconductive layer 34 overlying the conductive layer 32 ischarged in a dark environment by a conventional positive coronadischarge apparatus 36, schematically shown in FIG. 3b, which movesacross the layer 34 and charges it within the range of +200 to +700volts, +200 to +400 volts being preferred. The shadow mask 25 isidentified in the panel 12, and the positively-charged photoconductor isexposed, through the shadow mask, to the light from a xenon flash lamp38 disposed within a conventional three-in-one lighthouse (representedby lens 40 of FIG. 3c). After each exposure, the lamp is moved to adifferent position, to duplicate the incident angle of the electronbeams from the electron gun. Three exposures are required, from threedifferent lamp positions, to discharge the areas of the photoconductorwhere the light-emitting phosphors subsequently will be deposited toform the screen. After the exposure step, the shadow mask 25 is removedfrom the panel 12 and the panel is moved to a first developer 42 (FIG.3d). The first developer contains suitably prepared dry-powderedparticles of a light-absorptive black matrix screen structure material,and surface-treated insulative carrier beads (not shown) which have adiameter of about 100 to 300 microns and which impart a triboelectricalcharge to the particles of black matrix material, as described herein.

Suitable black matrix materials generally contain black pigments whichare stable at a tube processing temperature of 450° C. Black pigmentssuitable for use in making matrix materials include: iron manganeseoxide, iron cobalt oxide, zinc iron sulfide and insulating carbon black.The black matrix material is prepared by melt-blending the pigment, apolymer and a suitable charge control agent which controls the magnitudeof the triboelectric charge imparted to the matrix material. Thematerial is ground to an averge particle size of about 5 microns.

The black matrix material and the surface-treated carrier beads aremixed in the developer 42, using about 1 to 2 percent by weight of blackmatrix material. The materials are mixed so that the finely dividedmatrix particles contact and are charged, e.g., negatively, by thesurface-treated carrier beads. The negatively-charged matrix particlesare expelled from the developer 42 and attracted to thepositively-charged, unexposed area of the photoconductive layer 34, todirectly develop that area. Infrared radiation is then used to fix thematrix material by melting or thermally bonding the polymer component ofthe matrix material to the photoconductive layer, to form the matrix 23shown in FIGS. 2 and 3e.

The photoconductive layer 34 containing the matrix 23 is uniformlyrecharged to a positive potential of about 200 to 400 volts, for theapplication of the first of three color-emissive, dry-powdered, phosphorscreen structure materials. The shadow mask 25 is reinserted into thepanel 12, and selective areas of the photoconductive layer 34,corresponding to the locations where green-emitting phosphor materialwill be deposited, are exposed to visible light from a first locationwithin the lighthouse, to selectively discharge the exposed areas. Thefirst light location approximates the convergence angle of the greenphosphor-impinging electron beam. The shadow mask 25 is removed from thepanel 12, and the panel is moved to a second developer 42, containingsuitably prepared dry-powdered particles of green-emitting phosphorscreen structure material and surface-treated carrier beads. Thephosphor particles are surface-treated with a suitablecharge-controlling material as described herein. One thousand grams ofsurface-treated carrier beads are combined with 15 to 25 grams ofsurface-treated phosphor particles in the second developer 42. Thecarrier beads are treated to impart a e.g. positive, charge on thephosphor particles. The positively-charged green-emitting phosphorparticles are expelled from the developer, repelled by thepositively-charged areas of the photoconductive layer 34 and matrix 23,and deposited onto the discharged, light-exposed areas of thephotoconductive layer, in a process known as reversal developing. Thedeposited green-emitting phosphor particles are fixed to thephotoconductive layer by exposing the surface-treated phosphor toinfrared radiation which melts or thermally bonds the phosphor to thephotoconductive layer.

The process of charging, exposing, developing and fixing is repeated forthe dry-powdered, blue- and red-emitting, surface-treated phosphorparticles of screen structure material. The exposure to visible light,to selectively discharge the positively-charged areas of thephotoconductive layer 34, is from a second and then from a thirdposition within the lighthouse, to approximate the convergence angles ofthe blue phosphor- and red phosphor-impinging electron beams,respectively. The triboelectrically positively-charged, dry-powderedphosphor particles are mixed with the surface-treated carrier beads inthe ratio described above and expelled from a third and then a fourthdeveloper 42, repelled by the positively charged areas of the previouslydeposited screen structure materials, and deposited on the dischargedareas of the photoconductive layer 34, to provide the blue- andred-emitting phosphor elements, respectively.

In the preferred embodiment, the initial surface-treatment step includesforming a continuous coating of silicon dioxide (silica) on the surfaceof each phosphor particle, e.g., blue (ZnS/Ag), green (ZnS/Cu, Au, Al)and red (Y₂ O₂ S/Eu).

EXAMPLE 1

To provide this coating, 6.6 grams of a colloidal silica sol sold underthe trademark NYCOL 2030 EC (available from the PQ Corporation, Asland,MA 01721) are dissolved in 1 liter of isopropanol. One kilogram of bluephosphor, such as ZnS/Ag, is added to the solution and stirred for twohours to fully disperse the phosphor particles. The resulting continuoussilicon dioxide (silica)-coated phosphor particles are dried in a rotaryevaporator at a temperature of 85° C. until all the solvent is removedfrom the mixture. The silica-coated dried phosphor and a virgin uncoatedphosphor were tested for charge-to-mass ratio and screen weight bymixing 3 grams of phosphor with 150 grams of fluorosilanesurface-treated carrier beads. The fluorosilane-treated beads aretriboelectrically negative and thus induce positive charge on thephosphor particles. The test procedure is described herein, and theresults for the virgin phosphor (Z936 blue) and the silica coatedphosphor (Example 1) are listed in TABLE 1. The above-described silicacoating is also applied to the green (ZnS/Cu,Au,Al) phosphor and the redcore (Y₂ O₂ S/Eu) phosphor using the process steps described herein. Analternative collodial silica sol that may be used is sold under thetrademark Cab-O-Sperse grade-B (available from the Cabot Corporation,Tuscola, Ill.).

The silica coating on the phosphor particles provides a hydroxyfunctional group in the form of silanol. Silane or titanate couplingagents react with silanol groups to form covalent chemical bonds.Phosphors initially treated to provide a continuous silica coating andthen overcoated with a silane or titanate coupling agent have a surfacewith a functional organic group determined by the coupling agent used asthe overcoating. Such organic groups on surface-treated phosphors reactwith the functional groups provided on the carrier beads, as describedin the copending patent application entitled METHOD OF SURFACE TREATMENTOF CARRIER BEADS FOR USE IN ELECTROPHOTOGRAPHIC SCREEN PROCESSING, todetermine the magnitude of the triboelectric charge on thesurface-treated phosphor particles.

EXAMPLE 2

One-tenth (0.1) gram of N (2-aminoethyl-3-aminopropyl) methyldimethoxysilane (amino #1) is dissolved in 200 ml. of isopropanol toform a coating solution. One hundred grams of silica-coated bluephosphor particles, made by the process of example 1, are added to thecoating solution and ultrasonically stirred for about 10 minutes. Theaminosilane surface-treated blue phosphor is dried in a rotaryevaporator. The dried phosphor is then sieved through a 400 mesh screen.

Three (3) grams of dry-powdered, aminosilane surface-treated bluephosphor material are mixed with about 100 grams of fluoroslianesurface-treated carrier beads. The fluorosilane-treated beads aretriboelectrically negative and thus induce a positive charge on theaminosilane-treated blue phosphor particles. The charge-to-mass ratioand the electrophotographic screen (EPS)-characteristics (screen weightof the phosphor manufactured by this process were tested as describedherein, and the results are listed in TABLE 1.

EXAMPLE 3

Same as example 2, except that N-(aminoethyl aminopropyl)triethoxysilane (amino #2) replaces amino #1. All other materials andprocess steps are unchanged. Test results are listed in TABLE 1.

EXAMPLE 4

Same as example 2, except that 3-(aminopropyl)dimethyl-ethoxysilane(amino #3) replaces amino #1. All other materials and process steps areunchanged. Test results are listed in TABLE 1.

EXAMPLE 5

Same as example 2, except that (aminopropyl) triethoxysilane (amino #4)replaces amino #1. All other materials and process steps are unchanged.Test results are listed in TABLE 1.

EXAMPLE 6

Same as example 2, except that (methacryloxyproply)triethoxysilane(acrylo #6) replaces amino #1. All other materials and process steps areunchanged. Test results are listed in TABLE 1.

EXAMPLE 7

One-tenth (0.1) gram of isopropyl tri (dioctyl-pyrophosphato) titanate(Titanate) is dissolved in 200 ml of a 50:50 mixture of isopropanol andheptane to form a coating solution. One hundred grams of silica-coatedblue phosphor particles (from Example 1) are added to the coatingsolution and stirred for two hours. The titanate surface-treated bluephosphor is dried in a rotary evaporator, and the dried phosphor is thensieved through a 400 mesh screen. The test process is described herein,and the results are listed in TABLE 1.

EXAMPLE 8

One-tenth (0.1) gram of amino #1 is dissolved in 200 ml of isopropanolas described in example 1, to form a coating solution. One hundred gramsof silica-coated green phosphor particles are added to the coatingsolution and stirred for about two hours. The aminosilanesurface-treated green phosphor material is dried in a rotary evaporatorand then sieved through a 400 mesh screen.

Three (3) grams of the dry-powdered, aminosilane surface-treated greenphosphor material are mixed with 100 grams of fluorosilanesurface-treated carrier beads and tested as described herein. The testresults are listed in TABLE 2. A virgin green phosphor (ZnS/Cu,Au,Al)having neither a silica coating nor an aminosilane coating, is used as acontrol for green phosphors in Table 2.

EXAMPLE 9

Same as example 8, except that amino #2 replaces amino #1. All othermaterials and process steps are unchanged. The test results are listedin TABLE 2.

EXAMPLE 10

Same as example 8, except that amino #3 replaces amino #1. All othermaterials and process steps are unchanged. The test results are listedin TABLE 2.

EXAMPLE 11

Same as example 8, except that amino #4 replaces amino #1. All othermaterials and process steps are unchanged. The test results are listedin TABLE 2.

EXAMPLE 12

One-tenth (0.1) gram of amino #1 is dissolved in 200 ml of isopropanolto form a coating solution. One hundred grams of silica-coated redphosphor particles (Y₂ O₂ S/Eu) are added to the coating solution andstirred for about two hours. The aminosilane surface-treated redphosphor material is dried in a rotary evaporator and then sievedthrough a 400 mesh screen.

Three (3) grams of the dry-powdered, aminosilane surface-treated redphosphor material are mixed with 100 grams of fluorosilanesurface-treated carrier beads and tested as described herein. The testresults are listed in TABLE 2. A virgin red phosphor (Y₂ O₂ S/Eu) havingneither a silica coating nor an aminosilane coating, is used as acontrol for red phosphors in Table 2.

EXAMPLE 13

Same as example 12, except that amino #2 replaces amino #1. All othermaterials and process steps are unchanged. Test results are listed inTABLE 2.

EXAMPLE 14

Same as example 12, except that amino #3 replaces amino #1. All othermaterials and process steps are unchanged. Test results are listed inTABLE 2.

EXAMPLE 15

Same as example 12, except that amino #4 replaces amino #1. All othermaterials and process steps are unchanged. Test results are listed inTABLE 2.

                  TABLE 1                                                         ______________________________________                                        Virgin blue phosphors and silane-treated blue phosphors                       contacted with fluorosilane-treated glass beads for                           positively-charged phosphors.                                                                   Positive     EPS-Characteristics                            Type of           Charge-to-Mass                                                                             Screen. Wt                                     Phosphor                                                                              Coating   Ratio (μC/gm)                                                                           (mg/cm2)                                       ______________________________________                                        Blue    None      2.2          0.8                                            Example 1                                                                             Silica    4.2          1.5                                            Example 2                                                                             Amino #1  47           3.9                                            Example 3                                                                             Amino #2  35           3.1                                            Example 4                                                                             Amino #3  36           3.0                                            Example 5                                                                             Amino #4  21           2.1                                            Example 6                                                                             Acrylo #6 14           2.0                                            Example 7                                                                             Titanate  18           1.6                                            ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Virgin green and red phosphors and silane-treated green                       and red phosphors contacted with fluorosilane-treated                         glass beads for positively-charge phosphors                                                     Positive     EPS-Characteristics                            Type of           Charge-to-Mass                                                                             Screen. Wt                                     Phosphor                                                                              Coating   Ratio (μC/gm)                                                                           (mg/cm2)                                       ______________________________________                                        Green   None      0.2          0.5                                            Example 8                                                                             Amino #1  35           3.0                                            Example 9                                                                             Amino #2  38           3.5                                            Example 10                                                                            Amino #3  29           2.9                                            Example 11                                                                            Amino #4  25           2.0                                            Red     None      0.9          1.0                                            Example 12                                                                            Amino #1  45           4.1                                            Example 13                                                                            Amino #2  43           4.0                                            Example 14                                                                            Amino #3  40           3.5                                            Example 15                                                                            Amino #4  34           3.6                                            ______________________________________                                    

The test results were determined using a test panel, not shown, whichconsists of an insulated board having a metal conductor laminated oneach major surfac,e with a centrally disposed aperture extending throughthe major surfaces of the board and the conductors. Preferably, theaperture is about 2.54 cm in diameter. A metal screen of about 50 to 100mesh extends across the aperture and is connected to one of the metalconductors. A TIC-coated glass plate extends across the aperture and isdisposed on the other metal conductor, so that the TIC-coating is incontact therewith. For the measurement of positively-charged phosphorparticles, a potential of 100 to 600 volts is applied to the conductor,with the conductor which contacts the TIC coating being grounded. Thepotential difference between the mesh and the glass is about 10³ V/cm.The test panel is located about 7.62 cm above a developer containing thesurface-treated phosphor and carrier beads as described in examples 1,2, 7, 8 and 12. The developer is closed at one end by a screen suitablefor passing the finely divided phosphor particles, but not the carrierbeads. A puff of air (velocity about 10⁴ cm sec) separates the phosphorparticles from the carrier beads and expels the charged (in this casepositively-charged) phosphor particles from the developer towards themetal screen and TIC-coated glass plate. The resultant electrostaticcharge on the TIC-coated plate is measured by an electrometer, and themass of the phosphor particles is determined by weighing the glass platebefore and after the test. The quotient of these measurements is theaverage triboelectric charge-to-mass ratio. The deposition area on theTIC-coated glass plate is known and controlled by the size of theaperture in the test panel. Test results are summarized in TABLES 1 and2. In each instance, the surface-treated glass beads include a coatingof fluorosilane, to impart a positive charge to the phosphor particles.A control was run for each color phosphor tested. The control phosphorswere not surface-treated. The results demonstrate that thesurface-treated phosphors have a much higher charge-to-mass ratio thando the untreated phosphors, and that the screen weights forsurface-treated phosphors are substantially higher than for untreatedphosphors. Best results were achieved by surface treating the phosphorswith N-(aminoethyl aminopropyl)triethoxysilane orN(2-aminoethyl-3-aminopropyl) methyldimethoxysilane.

Other silanes found specifically useful are (n decyl) methyldichloro-silane,(heptadecafluoro-1,1,2,2-tetrahydrodecyl)-1-dimethyl-chlorosilane and(tridecafluorooctyl-1-dimethyl-triethylsilane.

What is claimed is:
 1. A method of surface-treating dry-powderedphosphor particles for use in manufacturing a viewing screen for a CRTto control the triboelectric charge characteristics of said phosphorparticles including the steps ofproviding said phosphor particles with afirst coating of silica, dissolving a coupling agent selected from thegroup consisting of silanes and titanates in a suitable solvent to forma mixture, surface-treating said silica-coated phosphor particles withsaid mixture to provide a second coating of said coupling agent thereon,filtering the surface-treated phosphor particles, rinsing the filteredsurface-treated particles in said solvent, and drying saidsurface-treated phosphor particles.
 2. The method of claim 1, whereinsaid mixture is formed by dissolving 0.1 gram of a silane selected fromthe group consisting of N(2-aminoethyl-3-aminopropyl) methyldimethoxysilane, N-(aminoethyl aminopropyl) triethoxysilane,3-(aminopropyl) dimethyl ethoxysilane, (aminopropyl) triethoxysilane,(methacryloxy propyl) trimethoxysilane, (n-decyl) methyldichlorosilane,(heptadecafluoro-1,1,2,2-tetrahydrodecyl)-1-dimethyl-chlorosilane and(tridecafluoro-1,1,2,2-tetrahydro octyl)-1-dimethyl-triethoxysilane, in200 ml of isopropanol.
 3. The method of claim 2, wherein said surfacecoating step includes the steps of(i) adding 100 grams of saidsilica-coated particles to said mixture, and (ii) ultrasonically mixingsaid silica-coated particles and said mixture for 10 minutes.